Why did My Multimeter Fuse Blow?

Introduction

A multimeter is something that we’ve all seen but many still don’t know how to use it. Checking your electronic system for faults was never this easy – simply grab your multimeter, set it to a required value and start measuring voltage, resistance, and current. Nowadays, you can find multimeters for less than 10 bucks and even this cheap piece of hardware can come in handy when you need to fault-chek your battery or any other device.

But, measuring voltage, resistance, and current is something that’s vastly different, even for your multimeter. When you don’t understand how a multimeter works, you can end up with a blown fuse. This means that your multimeter uses different techniques for measuring these 3 different variables. Trying to measure a certain value in a way that’s used for measuring a different value will cause your multimeter fuse to blow.

Why did my Multimeter Fuse Blow?

Well, as we said earlier; it blew as a result of misusing its functions. The multimeter comes with two inserts for positive leads. One insert has a function of measuring voltage while the other one is here to measure current. The insert that measures the voltage has a high resistive function and the current one has a low resistive function. Setting your lead to the voltage function will cause it to have a high resistance. In this case, the multimeter fuse will not blow even if the multimeter was set to measure current. This happens because as the energy is depleted, due to the high resistance.

However, setting your lead to the current function will produce the opposite reaction, which can cause your fuse to blow. This further means that you need to be careful about measuring the current. Measuring your current in parallel will, in most cases, immediately blow the fuse as the ammeter (part of a multimeter which measures current) has almost zero resistance. Despite carrying a great risk of blowing a fuse, this method will not always do that. It happens only if the current is strong enough to do it simply because the current is then directed in the direction of an ammeter.

Measuring the current inappropriately isn’t the only thing that will make your fuse blow. The same can happen even if you set your multimeter to measure current and you try to measure voltage. In this case, the resistance is minimal which allows the current to flow in the direction of the multimeter. Produced by the almost non-existing resistance, the current starts to produce too much energy for the multimeter and the fuse blows.

In case you switch the multimeter to measure voltage, it ‘assumes’ that resistance is very high, that little to no current will be let through.

To put it simply, measuring current inappropriately while your multimeter is set to amp function will cause the fuse to blow. Alternatively, the fuse can be blown by measuring voltage when your multimeter is still set to measure current.

How to Change the Fuse?

In case your multimeter fuse blows, you can easily replace it with minimal effort. Here’s how to do it:

  1. Grab your screwdriver and start taking out screws at the back.
  2. Remove two screws behind the battery plate.
  3. Carefully lift the front of the multimeter. Be sure not to pull or squeeze too hard.
  4. Usually, you’ll see two hooks on the bottom edge of the front panel. Simply slide the panel away sideways to disengage them.
  5. Once you unhook them, you should clearly see inside of the multimeter.

The fuse is usually located on the bottom part of the multimeter. Use a screwdriver or any other prying tool to lift off the broken fuse and replace it with the same one. It’s very important that you don’t go and buy a different fuse!

If you take off a 100mA fuse, you should always replace it with the exact same fuse – 100mA.

Changing the fuse is not a time-consuming process and we suggest that you do it if it’s needed. After all, the fuse will cost you a dollar or two and it’s a difference between life and death for your multimeter.

Conclusion

To put things into perspective, let’s see how you can prevent your fuse from blowing. First, always make sure to set your multimeter to measure voltage as this will prevent any potential blows. If you’re measuring current, be fully concentrated and don’t measure it in parallel. Those who use a multimeter for the first time will have a hard time getting used to it. The key factor is to always be concentrated and ask someone to help you if you don’t know what to do.

Despite the low price of this device, it’s very useful and you should definitely buy one for yourself.

Oh, and make sure not to blow the fuse!

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